ix PKOTECTIVE INOCULATION 271 



of these materials to protect similar rodents against 

 subsequent infection with virulent B. pestis. 



A considerable number of experiments and observations 

 were in the first instance made by me in order to ascertain 

 the best mode of preparing and preserving prophylactic 

 material of this nature, as well as to determine which 

 portions of the body of an animal dead of plague are the 

 most efficacious for the purpose. It is not necessary to 

 describe in detail here all the steps adopted ; they will be 

 fully dealt with in a forthcoming Eeport of the Medical 

 Officer of the Local Government Board. Suffice it to say 

 that they comprised experiments with — 



(a) Dried material of all the organs of mice, of guinea- 

 pigs, and of rats dead of acute virulent plague ; 



(6) Dried material of the bubo and spleen alone of 

 mice, guinea-pigs, and rats dead of acute plague ; 



(c) Dried material of all the organs of guinea-pigs 

 dead of subacute plague, i.e. of guinea-pigs in which 

 death occurred after four or five days with necrosis of the 

 bubo, necrotic nodules of the spleen, liver, and lungs ; 

 and 



(d) Dried material of those organs alone which showed 

 necrotic changes — that is, bubo, spleen, lungs, and liver of 

 guinea-pigs dead of subacute plague. 



These several materials were dried — 



(e) At the temperature of the laboratory over sulphuric 

 acid; 



(/) At the temperature of 20° C. over sulphuric acid ; 

 (g) At the temperature of 37° C. over sulphuric acid ; 

 (h) At the temperature of 46° to 47° C. over sulphuric 

 acid. 



The result of these experiments showed that a variety 



